Puja Ohri

Evaluation of in vitro and in vivo nematicidal potential of a multifunctional streptomycete, Streptomyces hydrogenans strain DH16 against Meloidogyne incognita

The present work demonstrated the nematicidal potential of Streptomyces hydrogenans strain DH16 (a strain with strong antagonism against fungal phytopathogens and insect pest) against Meloidogyne incognita. The culture supernatant and solvent extract significantly inhibited egg hatching (almost 100%) along with J2 mortality of more than 95% after 96h. The nematicidal activity of 10-(2,2-dimethyl-cyclohexyl)-6,9-dihydroxy-4,9-dimethyl-dec-2-enoic acid methyl ester (SH2; a new antifungal compound) purified from this streptomycete was also evaluated using different concentrations. The juvenile mortality of the nematode increased with increasing concentration and exposure time and reached the maximum (95%) after 96h at concentration of 100μg/ml. After 160h of incubation, egg hatch of 16% was observed at concentration of 100μg/ml as compared to control where 100% egg hatching was achieved. However, at the highest concentration of the compound (200μg/ml), 100% J2 mortality and 0% egg hatching were observed after 72 and 160h of incubation, respectively. In vivo pot experiments further revealed the nematicidal potential of S. hydrogenans where soil drenching with its culture supernatant and cells effectively controlled root galls, egg masses in nematode infested tomato plants and at the same time promoted the growth of tomato plants. Additionally, in the absence of nematodes, soil drenching with culture supernatant and cells significantly enhanced the various agronomic traits of plants as compared to control plants. Thus, the outcomes of the current study endorse the potential of S. hydrogenans strain DH16 and its metabolites to be developed as safe nematicidal and plant growth promoting agents.

Role of various hormones in photosynthetic responses of green plants under environmental stresses.

Environmental stress includes adverse factors like water deficit, high salinity, enhanced temperature and heavy metals etc. These stresses alter the normal growth and metabolic processes of plants including photosynthesis. Major photosynthetic responses under various stresses include inhibition of photosystems (I and II), changes in thylakoid complexes, decreased photosynthetic activity and modifications in structure and functions of chloroplasts etc. Various defense mechanisms are triggered inside the plants in response to these stresses that are regulated by plant hormones or plant growth regulators. These phytohormones include abscisic acid, auxins, cytokinins, ethylene, brassinosteroids, jasmonates and salicylic acid etc. The present review focuses on stress protective effects of plants hormones on the photosynthetic responses.

Jasmonic acid-induced tolerance to root-knot nematodes in tomato plants through altered photosynthetic and antioxidative defense mechanisms

Plant parasitic nematodes cause severe damage to cultivated crops globally. Management of nematode population is a major concern as chemicals used as nematicides have negative impact on the environment. Natural plant products can be safely used for the control of nematodes. Among various plant metabolites, plant hormones play an essential role in developmental and physiological processes and also assist the plants to encounter stressful conditions. Keeping this in mind, the present study was designed to evaluate the effect of jasmonic acid (JA) on the growth, pigments, polyphenols, antioxidants, osmolytes, and organic acids under nematode infection in tomato seedlings. It was observed that nematode inoculation reduced the growth of seedlings. Treatment with JA improved root growth (32.79%), total chlorophylls (71.51%), xanthophylls (94.63%), anthocyanins (37.5%), and flavonoids content (21.11%) when compared to inoculated seedlings alone. The JA application enhanced the total antioxidant capacity (lipid- and water-soluble antioxidants) by 38.23 and 34.37%, respectively, in comparison to infected seedlings. Confocal studies revealed that there was higher accumulation of glutathione in hormone-treated seedlings under nematode infection. Treatment with JA increased total polyphenols content (74.56%) in comparison to nematode-infested seedlings. JA-treated seedlings also enhanced osmolyte and organic acid contents under nematode stress. Overall, treatment with JA improved growth, enhanced pigment levels, modulated antioxidant content, and enhanced osmolyte and organic acid content in nematode-infected seedlings.

A Highly Selective Fluorescent Probe for Detection of Hydrogen Sulfide in Living Systems: in vitro and in vivo Applications

A fluorescein-based fluorescent probe has been designed and synthesised that selectively detects H2 S in aqueous medium, among various analytes tested. This fluorescein-based fluorescent probe has also been successfully utilised for real-time imaging of exo- and endogenously produced H2 S in cancer cells and normal cells. Moreover, the probe can also detect H2 S in the rat brain hippocampus at variable depths and in living nematodes.

Responses of Phytochelatins and Metallothioneins in Alleviation of Heavy Metal Stress in Plants: An Overview

Abstract Heavy metal detoxification in plants is a phenomenon resulting from complex interactions among interconnected physiological pathways and defense shunts leading to reactive oxygen species scavenging and subsequent protection of cellular vitals. These signaling pathways involve cross-talk between a number of antioxidant compounds including two main groups of amino acid rich metal chelators, namely the phytochelatins (PCs) and metallothioneins (MTs). This book chapter traces the mechanism of metal tolerance and detoxification strategies possessed by these biological molecules in addition to their biosynthesis, roles played and genetic aspects involved in their course of action. The isolation, characterization of PC and MT genes involved in metal compartmentalization and their successful induction in other plants is a much more recent application because this is of immense importance to the world of agronomics. Genetic validation and success for the same has been reported widely in this decade and many prominent reports have been included in the text to highlight this. Extending this vast information about the PC and MT gene pool at the proteomic level is gaining a lot of momentum currently and shall remain the future line of investigation for understanding metal resistance pathways at the cellular as well as subcellular level.

Interaction of Salicylic Acid with Plant Hormones in Plants Under Abiotic Stress

Plants are exposed to a number of abiotic stresses like salinity, heavy metals, temperature, drought, etc. which have adverse effects on their growth and yield. They have well-developed mechanisms which recognize various stress signals and manage the plants to grow under these stresses. Phytohormones play a major role in stress protection in plants by intervening growth, nutrient distribution, development, and source/sink transitions. In plants, interaction between various phytohormones results in positive and negative cross talk that play an essential role in response to abiotic stresses. Their biosynthetic pathways and mechanisms of action are interlinked. A complex hormone signaling and their ability to interact with each other make them optimal candidates for negotiating defense responses. Salicylic acid (SA) is an important plant growth regulator which regulates various physiological processes such as seed development, seed establishment, cell growth, senescence etc. in plants. The interaction of SA with other hormones like auxins, gibberellins, abscisic acid, ethylene, cytokinin, polyamines, jasmonic acid, and brassinosteroids play an important role in fine-tuning the network of immune response against abiotic stress.

ROS Signaling in Plants Under Heavy Metal Stress

Contamination of soil with toxic heavy metals is a major reason for retarded growth of crops and harmful effects on human health. Cultivation of large number of agricultural crops in contaminated soil is a major concern of environmentalist in the present times. Increased level of heavy metals can enter in to the food chain and may available for human consumption. Metal toxicity-induced oxidative stress eventually leads to refrained enzyme activities due to displacement of essential cofactors with other metal ions and blocking of functional groups such as carboxyl, histidyl and thiol, and proteins. Oxidative burst releases large quantities of reactive oxygen species (ROS) such as superoxide anion, hydrogen peroxide, hydroxyl radical, singlet oxygen, etc., which is one of the primary response of plants to heavy metal stress. Production of ROS is an inherent feature of plant cell and contributes to the process of oxidative damage leading to cell death. Its production is restricted to several cellular compartments such as mitochondria, chloroplast, and peroxisomes etc. ROS production leads to alteration of several physiological processes including degradation of enzymes, proteins, and amino acids and change in structure of cells. ROS are well described as secondary messengers in variety of cellular processes including acclimatization of cells to stress conditions. The signaling of ROS as a result of oxidative damage is regulated by several other signaling cascades which are interlinked. Their role has been studied under various stress conditions specifically heavy metals which leads to production of NO, H2O2, synthetic electrophilic compounds, lipid peroxidation molecules, etc.

Jasmonic acid induced changes in physio-biochemical attributes and ascorbate-glutathione pathway in Lycopersicon esculentum under lead stress at different growth stages

Lead (Pb) is one of most toxic heavy metals that adversely affect growth and developmental in plants. It becomes necessary to explore environment safe strategies to ameliorate its toxic effects. Phytohormones play an imperative role in regulating stress protection in plants. Jasmonic acid (JA) is recognized as a potential phytohormone which mediates immune and growth responses to enhance plant survival under stressful environment. The present study was undertaken to evaluate the effect of JA on the growth, metal uptake, gaseous exchange parameters, and on the contents of pigments, osmolytes, and metal chelating compounds in tomato plants under Pb stress during different stages of growth (in 30-, 45-, and 60-day-old plants). We observed a decrease in shoot and root lengths under Pb stress. Treatment of JA improved the shoot and root lengths in the Pb-treated plants. The Pb uptake was increased with the increasing concentrations of Pb, however, seeds pretreated with JA reduced the Pb uptake by the plants. The chlorophyll and carotenoid contents increased by JA treatment in plants under Pb stress. Pre-soaking of seeds in JA, improved gaseous exchange parameters, such as internal CO2 concentration, net photosynthetic rate, stomatal conductance, and transpiration rate under Pb stress. JA enhanced the enzyme activity of ascorbate-glutathione cycle and reduced H2O2 concentration in Pb-treated plants. The contents of osmolyte and metal chelating compounds (total thiols, and non-protein and protein-bound thiols) were increased with the increase in Pb stress. In seeds primed with JA, the contents of osmolytes and metal chelating compounds were further increased in the Pb-treated plants. Our results suggested that treatment of JA ameliorated the toxic effects of Pb stress by reducing the Pb uptake and improving the growth, photosynthetic attributes, activity of ascorbate-glutathione cycle and increasing the contents of osmolytes and metal chelating compounds in the tomato plants.

Emerging Role of Polyamines in Plant Stress Tolerance

Plants, being sessile organisms, are challenged by variety of stresses in the form of abiotic and biotic components of environment. In such adverse conditions, plants evolve various adaptive strategies in order to survive. Among these strategies, accumulation of polyamines in plants helps to combat stress. Polyamines are ubiquitous low molecular weight compounds, which are now known to be involved in stress tolerance as suggested by various pieces of evidence during abiotic and biotic stress. The anti-stress properties of polyamines in plants are illustrated by their roles in modulation of morphological growth parameters, elevation of photosynthetic pigments, as well as declined content of stress indices, antioxidative enzymes, and non-enzymatic antioxidants content. The emerging role of polyamines in plant stress tolerance has been discussed in the present review.

Emerging Trends in Physiological and Biochemical Responses of Salicylic Acid

Salicylic acid (SA) is one of the important plant growth regulators that has garnered focus due to its crucial role in both physiological aspects and plant defense responses. Several studies throw light on its role in regulation of various biochemical pathways that further shows its control on morphology and physiology of plants. It is involved in conferring innate immunity to plants against both biotic and abiotic stresses by influencing multiple processes. It interacts with transcription factors and thus alters gene expression. It is also instrumental in controlling the expression of PR genes through NPR1 proteins. RNA silencing mechanisms in viral infections also become activated with SA and thus provide immunity. Plants also gain systemic acquired resistance through SA that causes stimulation of long-distance mobile signaling and activation of transcriptional coactivators. The studies thus indicate that SA is involved in regulation of mechanisms responsible for plant morphology, physiology, and responses to stress.